The investigation of subjective time perception can be undertaken on a number of different levels. At each of these levels there are pieces of empirical evidence to suggest that perceptions of time may be sensitive to age-related changes. Thus, at the biological level circadian rhythmicity and speed of neural transmission are known to be subject to age modifications. At the psychological level, temporal sequencing of events and the ability to retain temporal information over short intervals of time decline with age; at the anatomical level, the central nervous structures purported to be influential for retaining temporal information show age-related cell loss; and finally, time disorientation is one of the prime manifestations of organic brain syndromes such as Alzheimer's disease. Even perceptions of social and historical time are hypothesized to be affected by the aging process. The intent of the present proposal is to directly investigate age- related changes in subjective time perception using an animal model. Research on the temporal aspects of animal memory has been given new impetus recently due to a variety of new testing methods for assessing these attributes. These procedures, using rat subjects, can reduce some of the confounds inherent in studying human time perception such as the role of past experience and verbal mediation behaviors. The proposal plan of research intends to study temporal processing by a) assessing the properties of the rat's internal clock and b) determining whether temporal sequencing of information is affected by increasng age. These studies, using both cross-sectional and longitudinal designs should provide valuable information as to whether age-related changes in time perception result from changes in an intrinsic physiological mechanism such as a clock, or are primarily due to age-related changes in the ability to encode contextual temporal information.